Energy Converter
Convert energy between joules, kilojoules, calories, kilocalories, watt-hours, kilowatt-hours, BTU and foot-pounds. Type a value and see it across every unit. A free, exact energy converter that runs in your browser.
Translate an energy figure between the units food labels, bills and engineers use. Convert kJ to kcal for a nutrition panel, kWh to joules for electricity, or BTU to kilowatts for heating, all from one value. Enter the number once and read every unit.
- Exact, standard factors
- 100% free
- No sign-up, no app
- Instant as you type
- Works offline after first load
1 kJ in every unit
How to use it
- 1
Enter a value
Type the energy you have, such as 2000 kJ or 1 kWh.
- 2
Choose the units
Set what you are converting from and to, then swap for the reverse.
- 3
Read every unit
See joules, calories, kilocalories, watt-hours, kWh and BTU together, and copy any line.
When it comes in handy
Food and diet
Convert between kilojoules and kilocalories, the two ways food energy is labelled in different countries.
Electricity bills
Switch between kilowatt-hours and joules to make sense of usage figures.
Heating and engineering
Convert BTU to kilowatt-hours or joules when sizing heating and cooling.
Instant, exact & 100% in your browser
The conversion runs right here in your browser using exact, standard factors. Nothing you type is sent to a server, there is no sign-up and no limit, and once the page has loaded it keeps working even with no connection.
Frequently asked questions
- What is the difference between a calorie and a kilocalorie?
- A kilocalorie is 1,000 calories. The confusing part is that food labels usually say "calories" but mean kilocalories, so a 200-calorie snack is really 200 kilocalories, or 200,000 small calories. This converter keeps them separate so you can be precise. One kilocalorie is about 4,184 joules.
- How many joules are in a kilowatt-hour?
- A kilowatt-hour is 3,600,000 joules, because one watt is one joule per second and there are 3,600 seconds in an hour. That is why kilowatt-hours, not joules, are used on electricity bills: the joule is simply too small a unit for household amounts.
- How do I convert kilojoules to kilocalories?
- Divide kilojoules by about 4.184 to get kilocalories, since one kilocalorie is 4.184 kJ. So a 2,000 kJ snack is roughly 478 kcal. Countries that label food in kJ and those that use kcal are describing the same energy in different units.
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